Direct spark ignition system with sampling flame sensor

ABSTRACT

An automatic fuel ignition system includes an ignition circuit for generating ignition sparks for igniting fuel discharged by a fuel outlet, an energizing circuit controlled by the ignition circuit to operate redundantly connected fuel valves to supply fuel to the fuel outlet, and a flame sensing circuit operable when a flame is established to normally disable the ignition circuit and to periodically enable the ignition circuit to test the operability of the ignition circuit. A light emitting diode, controlled by the energizing circuit, provides remote indication of the operability of the ignition circuit.

United States Patent Matthews 14 1 Oct. 21, 1975 DIRECT SPARK IGNITION SYSTEM WITH SAMPLING FLAME SENSOR Russell Byron Matthews, Goshen, Ind.

Inventor:

Assignee: Johnson Service Company,

Milwaukee, Wis.

Filed: Sept. 23, 1974 Appl. No.: 508,417

US. Cl. 431/66; 317/96; 431/80 1m. c1. r230 3/00 Field 01 Search 431/66, 67, 70, 71, 78,

References Cited UNITED STATES PATENTS 4/1969 Walbridge 431/66 7/1973 Finger 431/66 10/1973 Alessio 431/66 3,847,533 11/1974 Riordan 431/78 Primary Examine,rEdward G. Favors Attorney, Agent, 0r Firm-Johnson, Dienner, Emrich & Wagner [57] ABSTRACT An automatic fuel'ignition system includes an ignition circuit for generating ignition sparks for igniting fuel discharged by a fuel outlet, an energizing circuit controlled by the ignition circuit to operate redundantly connected fuel valves to supply fuel to the fuel outlet, and a flame sensing circuit operable when a flame is established to normally disable the ignition circuit and to periodically enable the ignition circuit to test the operability of the ignition circuit. A light emitting diode, controlled by the energizing circuit, provides remote indication of the operability of the ignition circuit.

17 Claims, 1 Drawing Figure T0 FUEL SOURCE U.S. Patent 0a. 21, 1975 momzow 53 OP DIRECT SPARK IGNITION SYSTEM WITH SAMPLING FLAME SENSOR BACKGROUND OF THE INVENTION 1. Field of the Invention.

This invention relates to automatic fuel ignition systems, and more particularly to a self-checking fuel ignition system providing automatic shut off of fuel in the event of loss of flame or ignition sparks.

2. Description of the Prior Art.

Automatic fuel ignition systems generally include an igniter circuit having a pulse generator operable when enabled to generate high voltage pulses which are applied to a pair of ignition electrodes positioned adjacent a fuel outlet. The ignition electrodes are spaced apart to provide a gap there between such that the high voltage pulses applied to the electrodes produce igni- 'tion sparks for igniting fuel emanating from the outlet to establish a flame. When the flame is established, a flame sensing circuit, which includes a second pair of electrodes, disables the pulse generator. In the event of a flame out, the flame sensing circuit reenables the pulse generator to attempt reignition of the fuel.

In certain igniter circuits, a pulsating control device is employed for disabling the pulse generator whenever a flame is established. In ignition systems energized from an AC voltage source, the cyclical AC voltage can be used to drive such control device. However, in ignition systems energized from a DC source, such as may be employed in a heating system for a mobile recreational vehicle, an inverter circuit is necessary to provide the required pulsating drive resulting in additional cost and complexity to the ignition circuit.

A further consideration is that in the event of a flame-out condition, reignition of I the fuel depends upon the operability of the spark generator of the igniter circuit. Thus, in the event of a malfunction of the spark generator, unburned gas will be wasted as the igniter circuit cycles to attempt reignition. Moreover, since the igniter circuit usually is located in an enclosure and is generally not readily accessible to view, failure of the spark generator may go unnoticed for a long period of time.

Accordingly, it would be desirable to have an automatic fuel ignition system in which the operability of the igniter circuit is continuously monitored. It would also be desirable to have an automatic fuel ignition system which indicates whether or not the igniter circuit is operating properly. Moreover, it would be desirable to be able to provide such indication at a location remote from the location of the igniter circuit.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an automatic fuel ignition system which provides automatic shut off of the fuelsupply in the event of loss of flame or loss of ignition sparks.

Another object of the invention is to provide a selfchecking fuel ignition system which automatically tests the operability of an ignition spark generator of the system.

A further object of the invention is to provide a fuel ignition system which permits remote indication of loss of spark and flame.

Another object of the invention is to provide an automatic fuel ignition system which employs a single pair of electrodes for both igniting the fuel to establish a flame and for sensing the presence of the flame.

A further object of the invention is to provide an automatic fuel ignition system having an inverter circuit which operates directly from a DC source.

These and otherobjects are achieved by the present invention which has provided an automatic fuel ignition system including ignition means operable when enabled to produce ignition sparks in the proximity of a fuel outlet, energizing means controlled by the ignition means to control the operation of valve means to supply fuel to the fuel outlet for ignition by the ignition sparks to establish a flame, and flame sensing means operable when a flame is established to normally disable the ignition means to inhibit the generation of ignition sparks and to periodically enable the ignition means when the flame is established to test the operability of the ignition means and the presence of flame.

In accordance with a disclosed embodiment, the ignition means includes oscillator means and enabling means for enabling the oscillator means to generate high voltage pulses for application to electrode means to produce ignition sparks. The oscillator means is energized from a DC source and employs feedback means to effect the generation of the voltage pulses. Accordingly, an inverter circuit is not required to convert DC input power to AC power in order to produce an alternating voltage for spark generation purposes.

The voltage pulses produced by the oscillator means also control the energizing means which includes a control means responsive to such pulses to effect operation of the valve means to supply fuel to the fuel outlet, and

sampling means enabled by the control means to maintain the valve means operated when a flame is established.

When a flame is established, the flame sensing means, which includes the electrode means, normally disables the oscillator means of the ignition means to inhibit spark generation, but periodically permits enabling of the oscillator means to test the operability of the oscillator means and to detect the presence of the flame to maintain the valve means operated.

When the oscillator means is disabled, the generation of voltage pulses is interrupted and thus, the control means is also disabled. However, the sampling means maintains the valve means operated whenever the control means is disabled as long as the control means continues to be periodically enabled by the ignition means under the control of the flame sensing means.

Should the flame fail to be established within a predetermined time, or for a flame-out condition, the control means effectsdeactivation of the valve means to interrupt the supply of fuel to the fuel outlet.

Only a single pair of electrodes is required to provide both ignition of the fuel and sensing of the resultant flame. The flame sensing means detects the presence of the flame.

In accordance with the present invention, an indicator means is controlled by the control means for pulsed operation each time an ignition spark is generated. In the event the oscillator means fails to operate when enabled by the flame sensing means, the indicator means is continuously energized to indicate failure of the oscillator means. Moreover, upon loss of ignition spark, the control means deactivates the valve means to interrupt the supply of fuel to the fuel outlet.

DESCRIPTION OF PREFERRED EMBODIMENTS General Description Referring to the drawing, there is shown a schematic circuit diagram of the self-checking automatic fuel ignition system provided by the present invention which, for example, may be used in a heating system for recreational vehicles. The fuel ignitionsystem 10 includes a pulse generating circuit 11 which effects the generation of ignition sparks between a pair of electrodes 12a and 12b located in the proximity of a main burner 18, for igniting gaseous fuel supplied to the burner 18. The pulse generating circuit 11 includes a control transistor 14 which supplies base drive current to a transistor 16 which together with windings 51 and 52 of an ignition transformer T1 comprise an oscillator circuit operable to produce high voltage pulses for application to the electrodes 12a and 12b to produce the ignition sparks.

Fuel is supplied to the main burner 18 whenever a main valve 19 and a redundant valve 20 are operated. The redundant valve 20 has an operate winding 28 connected in series with normally closed contacts 29 of a warp switch and normally closed contacts 41 of a limit switch (not shown)between conductors 42 and 43 over which the system 10 is energized such that the redundant valve 20 is normally maintained operated when the thermostat is calling for heat.

The main valve 19 has a pickup winding 27 which is energized by a control circuit 22 to operate the valve 19 to supply fuel to the burner 18 for ignition by ignition sparks to establish a flame. The control circuit 22 is in turn controlled by the pulse generating circuit 11. The control circuit 22 includes a pair of transistors 23 and 24, connected in Darlington configuration, which are pulsed into conduction by pulses provided by oscillator transistor 16 whenever the pulse generating circuit 11 is enabled. Energizing current is supplied to the pickup winding 27 of the main valve 19 whenever transistors 23 and 24 areconducting. The control transistors 23 and 24 also energize a warp switch heater 38 which controls the operation of a warp switch contacts 29. In the event of a flame-out condition or loss of ignition sparks through failure of the pulse generating circuit 11, the warp switch heater 38 operates associated contacts 29 to deenergize winding 28 of the redundant valve 20 to deactivate the valve 20 thereby interrupting the supply of fuel to the burner 18.

A sampling circuit 32, enabled by the control circuit 22 energizes a hold winding 36 of the main valve 19 to maintain the valve 19 operated when a flame is established. The sampling circuit 32 includes redundant transistors 33 and 34 and an integrating network 35 controlled by pulses supplied by the control transistors 23 and 24 to maintain the hold winding 36 of the valve 19 energized when the flame is established, The use of redundant transistors 33 and 34 assures that the hold winding 36 of the main valve 19 can be deenergized. Thus, should one of the transistors 33 or 34 become short-circuited from emitter to collector, the hold winding 36 will be deenergized when the other transistor is cutoff during normal operation of the sampling circuit 32.

In an alternative embodiment, the windings 27 and 36 may be windings of a two winding relay (not shown) and a control winding of the valve 19 may be connected in series with normally open contacts of the relay between point 55 and conductor 43, the control winding being energized to operate the valve 19 Whenever winding 27 or 36 is energized causing the relay to operate.

For the purpose of controlling the operation of the pulse generating circuit 11 when the flame is established such that the operability of the pulse generating circuit 11 can be tested periodically, the electrodes 12a and 12 b are connected in a flame sensing circuit 31 which senses the presence of the flame. Thus, the electrodes 12a and 12b are used to both ignite the fuel and to sense the presence of the flame. The flame sensing circuit 31 enables the fuel ignition system 10 to operate in a sampling mode in which the pulse generating circuit 11 and the control circuit 22 are normally disabled but are periodically enabled during sampling periods defined by the charging time of capacitor 40 of the flame sensing circuit 31. Capacitor 40, which is alternately charged and discharged whenever the flame is established, provides a control potential for enabling a transistor 39 of the flame sensing circuit 31 to conduct to disable the control transistor 14 after a first period during which the capacitor 40 charges.

During a second period, while capacitor 40 discharges, the pulse generating circuit 11 and the control circuit 22 are disabled. At the end of the second duration, capacitor 40 again charges while transistor 39 is cutoff such that the pulse generating circuit 1 1 is reenabled to produce further ignition sparks. At such time, pulse provided by the pulse generating circuit llenable the control circuit 22 to supply pulses to the sampling circuit 32 to maintain the main valve 19 operated as will be described hereinafter.

The periodic disabling of the control circuit 22 limits current flow through the warp switch heater 38 and the pick-up winding 27 of the main valve 19. With the presence of a flame at the electrodes 12a and 12b, the current flowing through winding 27 and warp switch heater 38 is only a fraction of that without the flame. Accordingly, heating of the warp switch heater 38 is negligible when a flame is established so that warp switch contacts 29 remain closed to energize the redundant valve winding 28.

Moreover, the average current through the pick-up winding 27 of the main valve 19 is maintained at a low value, the main valve 18 being held open by the hold winding 36 which is energized by the sampling circuit 32.

The periodic disabling of the control circuit 22 enables control pulses to be provided for the sampling circuit 32 permitting transistors 33 and 34 to be maintained conductive to maintain the main valve 18 operated.

The control circuit 22 further includes a visual indicating device 30, embodied as a light emitting diode, which permits a loss of spark condition to be indicated at a remote location remoted from the ignition circuit. Thus, while the electrodes must be positioned adjacent the main burner 18 which is generally enclosed and not readily accessible, the light emitting diode 30 may be located on the outside of the heating unit which employs the fuel ignition system 10 of the present invention.

When the fuel ignition system 10 is operating in the sampling mode, the light emitting diode 30 is pulsed on by the control circuit 22 each time an ignition spark is generated as transistors 23 and 24 of the control circuit 22 are periodically rendered conductive and nonconductive through operation of the flame sensing circuit 31.

In the event of loss of spark caused by a malfunction of the pulse generating circuit 11, or a short circuit between the electrodes 12a and 12b, transistor 25 of the pulse generating circuit 11 enables the control transistors 23 and 24 to conduct continuously to energize the warp switch heater 38 causing deactivation of the redundant valve 20 and to maintain the light emitting diode 30 continuously on to indicate the loss of spark condition.

Detailed Description Power is supplied to the fuel ignition system from a DC voltage source 41 which is connectable to a pair of conductors 42 and 43 over switch contacts SW which may be thermostatically controlled. In an exemplary embodiment, the voltage source is a 12 volt battery. When the contacts SW are closed, conductor 42 is connected to the positive terminal 44 of the voltage source 41. Conductor 43 is connected to the negative terminal 45 of the voltage source 41 which is connected to ground.

Transistor 14 of the pulse generating circuit 11 is connected in an enabling circuit between conductors 42 and 43. The emitter of transistor 14 is connected through a resistor 47 to conductor 42 and the collector of transistor 14 is connected through series connected resistors 48 and 49 to conductor 43. The base of transistor 14 is connected through resistor 50 to conductor 43. Transistor 14 is normally conducting when switch contacts SW are closed, supplying base current to transistor 16 of the oscillator circuit over resistor 48 and a feedback winding 51 of the ignition transformer T1, which is connected between the base of transistor 16 and the junction of resistors 48 and 49 at point 54. The collector of transistor 16 is connected through the primary winding 52 of the ignition transformer T1 to point 55 and over normally closed limit switch contacts 41 and warp switch contacts 29 to conductor 42. The emitter of transistor 16 is connected to conductor 43.

The base drive supplied to transistor 16 by transistor 14 enables transistor 16 to begin to conduct permitting current flow through the primary winding 52 of the ignition transformer T1, providing regenerative feedback to the base of transistor 16 until saturation is attained. At such time, the primary flux begins to decrease generating a reverse voltage in the feedback Winding 51 which tends to cutoff transistor 16 reducing the feedback, permitting transistor 16 to again be driven to saturation and the cycle repeats. The oscillating current in the primary winding 52 generates alternating high voltage pulses in the secondary winding 53 for application to the electrodes 12a and 12b.

The high voltage secondary winding 53 of the ignition transformer T1 is connected in a series circuit path with the ignition electrodes 12a and 12b between the conductors 42 and 43. More specifically, one end 56 of secondary winding 53 is connected through capacitor 40 and resistors 58 and 59 to conductor 42. The other end 57 of secondary winding 53 is connected to electrode 12a. The other ignition electrode 12b is connected to conductor 43. A capacitor 61 is connected between the junction of capacitor 40 and end 56 of secondary winding 53 and conductor 43. The electrodes 12a and 12b are spaced apart to provide a gap 62 there between to permit the generation of ignition sparks in the gap 62 whenever high voltage pulses are applied to the electrodes 12a and 12b over the secondary winding 53.

The pulses provided at the collector of transistor 16 of the pulse generating circuit 11 also enable transistors 23 and 24 of the control circuit 22 to effect operation of the main valve 19 by energizing the pick-up winding 27, which is a low resistance winding enabling fast operation of the valve 19. Transistors 23 and 24 are connected in Darlington configuration with the base of transistor 23 being connected to the emitter of transistor 24 and the collector of transistor 23 being connected to the collector of transistor 24. The emitter of transistor 23 is connected to conductor 42. The base of transistor 24 is connected over resistors 66 and 67 and diode 68 to, the collector of transistor 16. A capacitor 69 is connected between the junction of resistors 66 and 67 at point 70 and conductor 43.

Whenever transistor 16 is conducting, transistors 23 and 24 also conduct to supply energizing current to the pickup winding 27 and the warp switch heater 38. Thus, when switch SW is operated to enable the pulse generating circuit 11 to generate ignition sparks, the control circuit 22 effects operation of the main valve 19. As shown in the drawing, the main valve 19 and the redundant valve 20 are connected in series between a fuel source (not shown) and the main burner 18. Since the operate winding 28 of valve 20 is connected in series with normally closed warp switch contacts 29 and the normally closed limit switch contacts 41, the redundant valve 20 is normally operated whenever power is applied to conductors 42 and 43. Thus, gaseous fuel is supplied to the main burner 18 when the main valve is operated. In the event the gas discharged by the main burner 18 is not ignited within a predetermined time, the Warp switch heater 38 operates contacts 29 to effect deactivation of the redundant valve 20 to interrupt the supply of fuel to the main burner 18.

The sampling circuit 32 includes redundant transistors 33 and 34, the base electrodes of transistors 33 and 34 being connectedthrough resistors 72 and 74, respectively, and suitably poled diode 76 to the collector of transistor 24 to receive the enabling signals. The hold winding 36 of the main valve 19 is connected in an energizing circuit between the collector of transistor 33 and conductor 42, the emitter of transistor 33 being connected to the collector of transistor 34 and the emitter of transistor 34 being connected to conductor 43. Thus, the hold winding 36 is energized whenever transistor 33 and 34 are conducting. Once rendered conductive, transistors 33 and 34 are maintained conductive by an integrating network 35 which includes resistor and capacitor 78 which are connected in series between the junction of resistors 72 and 74 and diode 76 at point 81. The integrating network 35, including capacitor 78 and resistor 80, responds to the enabling signals provided by the control circuit 22 to maintain a potential at point 81 sufficient to maintain transistors 33 and 34'conducting for a duration defined by the values of capacitor 78 and resistor 80.

When ignition of the gas discharged by the main burner 18 is accomplished, the sensing circuit 31 including electrodes 12a and 12b senses the presence of the flame which bridges the gap 62 between the electrodes 12a and 12b and the system begins to operate in the sampling mode.

As indicated above, capacitor 40 of the flame sensing circuit 3i charges and discharges through the flame, providing a control potential for rendering transistor 39 alternately conductive and non-conductive. Transistor 39 in turn controls the conductivity of transistor 14 of the pulse generating circuit 11 to normally inhibit spark generation by cutting off oscillator transistor 16 when the flame is established, but to periodically enable spark generation by supplying base drive to transistor 16 to test the operability of the pulse generating circuit 11.

Diode 60, secondary winding 53 and the electrodes 12a and 12b form a portion of a charging path for capacitor 40. Diode 60 is connected between one side 83 of capacitor 40 and conductor 42. The other side of capacitor 40 is connected through secondary winding 53 to electrode 120. Whenever a flame bridges the gap 62 between the electrodes 12a and 12b, capacitor 40 charges over a path which extends from one side 83 of the capacitor 40, through diode 60 to conductor 42, through the battery 41 to conductor 43 and over electrodes 12a and 12b and the flame and through secondary .winding 53 to the other side 84 of capacitor 40.

Capacitor 40 then discharges over a path including transistor 39 to cause transistor 39 to conduct. The emitter of transistor 39 is connected through a resistor 85 and suitably poled diode 86 to conductor 42. The base of transistor 39 is connected to the junction of resistors 58 and 59, and the collector of transistor 39 is connected to the base of transistor 14 and over resistor 50 to conductor 43.

As capacitor 40 discharges, current flows from side 84 of capacitor 40 through secondary winding 53, electrodes 12a and 12b and the flame to conductor 43, through the battery 41, to conductor 42, through diode 86, resistor 85 the emitter-base circuit of transistor 39 and through resistor 58 to the other side 83 of capacitor 40. The discharge current flowing through transistor 39 causes transistor 39 to conduct, raising the base potential at the base of transistor 14 causing transistor 14 to be cut off, interrupting the flow of base current to oscillator transistor 16 to temporarily inhibit the generation of high voltage pulses. This condition exists for a time until the charge has leaked off capacitor 40, which for example, may take approximately to 20 seconds. Then transistor 39 becomes cutoff allowing transistor 14 to conduct to turn on transistor 16 permitting spark generation for approximately one second at which time the cycle repeats.

The light emitting diode 30 which provides a visual indication of the operability of the pulse generating circuit 11, is connected in series with a current limiting resistor 88 between the collector of transistor 24 of the control circuit 22 and conductor 43. Under normal operating conditions, the light emitting diode 30 flashes every time a spark is generated, approximately every 15 to 20 seconds, when control transistors 23 and 24 are rendered conductive in response to operation of the pulse generating circuit 11.

In the event electrodes 12a and 12b become shorted or should a malfunction occur in the pulse generating circuit 11, transistor 25 of the control circuit 22 effects continuous energization of the light emitting diode to indicate a failure.

Transistor 25 has a base electrode connected through resistor 91 to the junction of resistors 48 and 49 in the collector circuit of transistor 14. The collector of transistor 25 is connected through resistors 92 and 67 and 66 to the base of transistor 24. The emitter of transistor 25 is connected to conductor 43.

For a loss of spark condition, transistor 14 is rendered conductive, causing transistor 25 to turn on. Transistor 25 in turn enables transistors 23 and 24 to turn on energizing the light emitting diode 30. The warp switch heater 38 is also energized to permit contacts 29 to operate deactivating the redundant valve 20 to interrupt the supply of fuel to the main burner 18.

Operation Assuming initially that the main valve 19 is unoperated and that warp switch contacts 29 and limit switch contacts 41 are closed so that the redundant valve 20 operates, when the switch contacts SW are closed and the 12 volt potential provided by the battery 41 is applied to conductors 42 and 43. Accordingly, current flows from conductor 42 over resistor 47 and the emitter-base circuit of transistor 14 and thence over resistor 50 to conductor 43 causing transistor 14 to conduct. When transistor 14 conducts, collector current flows through resistor 48 and the feedback winding 51 of the ignition transformer T1 to the base and out the emitter of transistor 16 to conductor 43, causing transistor 16 to begin to conduct. Accordingly, current flows over warp switch contacts 29, limit switch contacts 41 and through the primary winding 52 of the ignition transformer T1 and the collector-emitter circuit of transistor 16 to conductor 43. The flux generated as the result of such current flow induces a voltage in the feedback winding 51 resulting in an increase in the conduction of transistor 16 with an attendant increase in collector current and thus the feedback voltage until transistor 16 is driven to saturation.

When transistor 16 is saturated, a feedback voltage is no longer induced in the feedback winding 51 and the primary flux in winding 52 begins to decrease causing a reverse voltage to be generated in feedback winding 51 which tends to cutoff transistor 16. This in turn reduces the feedback and thus base current for transistor 16 starts to flow again to repeat the cycle. The net effect is an oscillating current in the primary winding 52 which generates alternating high voltage pulses on the order of IOKV to 12KV in the secondary winding 53. Each voltage pulse thus produced causes a spark to jump from electrode 12a to electrode 12b to ground.

When transistor 16 is conducting, current flows from conductor 42 over the emitter-base circuit of Darlington connected transistors 23 and 24 and through resistors 66 and 67, diode 68, and the collector-emitter circuit of transistor 16 to conductor 43, causing transistors 23 and 24 to conduct to supply collector current to the warp switch heater 38 and the pickup winding 27 of the main valve 19. When the pickup winding 27 is energized, the main valve 19 is operated supplying gaseous fuel to the main burner 18. It is pointed out under normal conditions, ignition occurs before heating of the warp switch heater 38 is sufficient to cause operation of the warp switch contacts 29 as would deactivate the redundant valve 20.

In addition, when transistors 23 and 24 conduct, charging current for capacitor 78 of the sampling circuit 32 flows through diode 76, capacitor 78 and resistor 80, establishing a potential at point 81 sufficient to cause transistors 33 and 34 to turn on, energizing the hold winding 36 of the main valve 19.

As soon as the gas discharged by the main burner 18 is ignited, the presence of the flame is sensed by the flame sensing circuit 31 which enables the fuel ignition system 10 to operate in the sampling mode during which the pulse generating circuit 11 is enabled for one second intervals to produce ignition pulses for generating ignition sparks and is disabled for l5 to 20 second intervals after each pulse generation period.

When end 56 of secondary winding 53 becomes positive, current flows through capacitor 40, diode 60, conductor 42 through the battery 41 and over conductor 43 to the electrodes 12a and 12b through the flame to electrode 12a and through secondary winding 53, placing a charge on capacitor 40. Capacitor 40 then starts to discharge with discharge current flowing from one side of capacitor 40 at point 84 through secondary winding 53, the flame, conductor 43, the battery 41, conductor 42, diode 86, resistor 85 the emitter-base circuit of transistor 39 and resistor 58 to the other side of capacitor 40 at point 83. The discharge current causes transistor 39 to conduct permitting current flow through resistor 50 thereby increasing the potential at the base of transistor 14, such that transistor 14 cuts off, in turn cutting off transistor 16 to inhibit further spark generation. The discharge time of capacitor 40 is approximately 15-20 seconds after which time transistor 39 is cut off, allowing transistor 14 to conduct to reenable transistor 16 for approximately one second while capacitor 40 charges and the cycle repeats.

During the one second intervals in which transistor 16 oscillates, the control transistors 23 and 24 are pulsed on and off supply current pulses to the warp switch heater 38 and the pick-up winding 27. Also, the light emitting diode 30 flashes every time a spark is generated. However, as long as pulses are provided at 15 to second intervals, such pulses do not cause heating of the warp switch heater 38 to a point where deactivation of the redundant valve 20 is effected.

The pulses supplied to the warp switch heater 38 and pick-up winding 27 are also supplied to the integrating network 35 of the sampling circuit 32 so that capacitor 78 remains charged to a potential sufficient to maintain transistors 33 and 34 conducting to hold the main valve 19 open.

If the gas discharged by the main burner 18 fails to ignite or fails to be reignited in the event of a flame out condition, the pulse generating circuit 11 continues to operate and the current supplied to the warp switch heater 38 eventually heats to a point at which warp switch contacts 29 operate to deactivate the redundant valve 20 to shut off the supply of fuel to the main burner 18.

As indicated above, the light emitting diode 30 flashes every time a spark is generated, approximately every 15 to 20 seconds. In the event of a failure of the pulse generating circuit 11, the light emitting diode'30 is maintained continuously on to indicate such failure. For a loss of spark condition, transistor 14 will conduct. Assuming oscillator transistor 16 is open circuited, when transistor 14 conducts, transistor is turned on :due to the voltage drop across resistor 49. Conduction of transistor 25 causes transistor 23 and 24 to conduct energizing the warp switch heater 38 to effect shut off of the redundant valve 20 and to energize the light emitting diode 30.

Thus, the fuel ignition system 10 responds to two failures, Loss of flame for any reason or any failure that simulates loss of flame results in operation of the warp switch contacts 29 to deactivate the redundant valve 20. Loss of spark for any reason, including shorted electrodes, results in operation of the warp switch contacts 29 to shut off the redundant valve 20 and the continuous energization of the light emitting diode 30 to indicate the failure.

I claim:

1. In a fuel ignition system including valve means operable when energized to supply fuel to a fuel outlet, an ignition circuit for controlling the operation of said valve means and for igniting fuel discharged by said fuel outlet, said ignition circuit comprising ignition means operable when enabled to generate ignition sparks in the proximity of said fuel outlet, energizing means controlled by said ignition means to energize said valve means to supply fuel to said fuel outlet for ignition by said ignition sparks to establish a flame, sensing means enabled whenever a flame is established to disable said ignition means during a first period to inhibit the generation of ignition sparks and for enabling said ignition means to generate ignition sparks during a second period, and indicator means controlled by said energizing means to provide a first indication each time an ignition spark is generated, and to provide a second indication whenever said ignition means fails to produce ignition sparks during said second period.

2. A fuel ignition system as set forth in claim 1 wherein said energizing means includes first switching means enabled by said ignition means to effect operation of said indicator means, said ignition means being operable when enabled to provide control pulses for said first switching means effecting pulsed operation of said first switching means to permit said indicator means to operate each time an ignition spark is generated.

3. A fuel ignition system as set forth in claim 2 wherein said ignition means includes means for continuously enabling said first switching means whenever said ignition means fails to produce ignition sparks during said second period to provide continuous operation of said indicator means.

4. A fuel ignition system as set forth in claim 2 wherein said indicator means comprises a light emitting diode which is normally energized to emit light intermittantly in correspondance with the generation of ignition sparks and which is continuously energized whenever said ignition means fails to produce ignition sparks during said second period.

5. in a fuel ignition system including valve means for supplying gaseous fuel to a fuel outlet, an ignition circuit for controlling the operation of said valve means and for igniting fuel discharged by said fuel outlet, said ignition circuit comprising ignition means including electrode means, oscillator means, and enabling means for enabling said oscillator means to generate high voltage pulses for application to said electrode means to produce ignition sparks in the proximity of said fuel outlet, energizing means controlled by said ignition means for controlling said valve means to permit fuel to be supplied to said fuel outlet for ignition by said ignition sparks to establish a flame, flame sensing means including said electrode means operable when a flame is estblished to disable said enabling means for a first period whereby said oscillator means is disabled for 11 said first period, said flame sensing means'enabling said enabling means for a second period to therebyenable said oscillator means to generate further voltage pulses, and means enabled by said enabling means whenever said oscillator means fails to produce voltage pulses during said second period to enable said energizing means to control said valve means to interrupt the supply of fuel to said fuel outlet.

6. A fuel ignition system as set forth in claim which includes means for supplying a DC energizing potential to said ignition circuit to permit said enabling means to normally extend a DC enabling signal to said oscillator means, said oscillator means being responsive to said DC enabling signal to produce AC voltage pulses in an output circuit thereof, first means for coupling said voltage pulses to said electrode means to effect the generation of ignition sparks and second means for coupling said voltage pulses to said energizing means to permit energization of said valve means.

7. A fuel ignition system as set forth in claim 6 wherein said oscillator means comprises semiconductor means, said first means comprising a transformer means having a first winding connected to extend siad DC enabling signal to a control input of said semiconductor means, a second winding connected to said electrode means, and third winding connected in an output circuit of said semiconductor means to permit said voltage pulses to be coupled to said second winding.

8. A fuel ignition system as set forth in claim 5 wherein said flame sensing means includes switching means operable when enabled to inhibit said'enabling means and timing means operable whenever a flame is established to enable said switching means for said first duration and to disable said switching means for said second duration.

9. A fuel ignition system as set forth in claim 8 wherein said timing means includes capacitor means, first circuit means including said electrode means for permitting said capacitor means to charge over a first circuit path whenever a flame is established, and second circuit means including said switching means and said electrode means for permitting said capacitor means to discharge over a second circuit path to thereby operate said switching means, the discharge time of said capacitor means being greater than the charge time of said capacitor means whereby the first duration for which the oscillator means is inhibited is gerater than the second duration for which said oscillator means is enabled.

10. A fuel ignition system as set forth in claim 6 wherein said energizing means includes control means having first switching means responsive to said voltage pulses to provide further pulses for energizing a control winding of said valve means for operating said valve means to supply fuel to said fuel outlet for ignition by said ignition sparks, and sampling means having second switching means and timing means responsive to said further pulses to energize a further control winding of said valve means to maintain said valve means operated when a flame is established.

11. In a fuel ignition system including normally unoperated first valve means and normally operated second valve means connected in series between a fuel source and a fuel outlet, an ignition circuit for controlling the operation of saidfirst and second valve means to supply fuel to said fuel outlet and for igniting fuel discharged by said fuel outlet, said ignition circuit comprising ignition means including first means operable when enabled to generate ignition sparks in the proximity of said fuel outlet for igniting fuel discharged by said fuel outlet to establish a flame, and second means for enabling said first means, energizing means controlled by said first means for effecting the operation of said first valve means, and sensing means operable whenever a flame is established to control said second means to disable said first means for a first period to thereby inhibit the generation of ignition sparks and to enable said first means for a second period to permit the generation of further ignition sparks, said ignition means including third means enabled by said second means whenever said first means fails to be enabled during said second period to effect deactivation of said second valvemeans to interrupt the supply of fuel to saidfuel outlet.

12. A fuel ignition system as set forth in claim 11 which includes indicator means controlled by said energizing means to provide an indication each time a spark is generated.

13. A fuel ignition system as set forth in claim 11 wherein said energizing means includes control means having first switching means enabled by said first means to energize a pickup winding of said first valve means to operate said first valve means to supply fuel to said fuel outlet for ignition by said ignition sparks, and sampling means including second switching means enabled by said first switching means to energize a hold winding of said first valve means to maintain said first valve means operated when a flame is established.

14. A fuel ignition system as set forth in claim 11 wherein said energizing means includes control means having first switching means, said first means including means for generating control pulses to enable said first switching means to provide current pulses for effecting operation of said first valve means, said first switching means being disabled during said first period when the flame is established, and sampling means including second switching means and timing means responsive to said current pulses to provide a potential for enabling said second switching means to maintain said valve means operated duringsaid first period.

15. A fuel ignition system as set forth in claim 14 which includes third switching means energized by said first switching means to deactivate said second valve means whenever a flame fails to be established after a predetermined number of control pulses have been supplied to said first switching means by said first means.

16. A fuel ignition system as set forth in claim 15 which includes indicator meansenergized by each current pulse provided by said first switching means.

17. A fuel ignition system as set forth in claim 16 wherein said third means is enabled by said second means to continuously energize said second switching means whenever said first means fails to produce said control pulses during said second period to thereby effect continuous energization of said indicator means. 

1. In a fuel ignition system including valve means operable when energized to supply fuel to a fuel outlet, an ignition circuit for controlling the operation of said valve means and for igniting fuel discharged by said fuel outlet, said ignition circuit comprising ignition means operable when enabled to generate ignition sparks in the proximity of said fuel outlet, energizing means controlled by said ignition means to energize said valve means to supply fuel to said fuel outlet for ignition by said ignition sparks to establish a flame, sensing means enabled whenever a flame is established to disable said ignition means during a first period to inhibit the generation of ignition sparks and for enabling said ignition means to generate ignition sparks during a second period, and indicator means controlled by said energizing means to provide a first indication each time an ignition spark is generated, and to provide a second indication whenever said ignition means fails to produce ignition sparks during said second period.
 2. A fuel ignition system as set forth in claim 1 wherein said energizing means includes first switching means enabled by said ignition means to effect operation of said indicator means, said ignition means being operable when enabled to provide control pulses for said first switching means effecting pulsed operation of said first switching means to permit said indicator means to operate each time an ignition spark is generated.
 3. A fuel ignition system as set forth in claim 2 wherein said ignition means includes means for continuously enabling said first switching means whenever said ignition means fails to produce ignition sparks during said second period to provide continuous operation of said indicator means.
 4. A fuel ignition system as set forth in claim 2 wherein said indicator means comprises a light emitting diode which is normally energized to emit light intermittantly in correspondance with the generation of ignition sparks and which is continuously energized whenever said ignition means fails to produce ignition sparks during said second period.
 5. in a fuel ignition system including valve means for supplying gaseous fuel to a fuel outlet, an ignition circuit for controlling the operation of said valve means and for igniting fuel discharged by said fuel outlet, said ignition circuit comprising ignition means including electrode means, oscillator means, and enabling means for enabling said oscillator means to generate high voltage pulses for application to said electrode means to produce ignition sparks in the proximity of said fuel outlet, energizing means controlled by said ignition means for controlling said valve means to permit fuel to be supplied to said fuel outlet for ignition by said ignition sparks to establish a flame, flame sensing means including said electrode means operable when a flame is estblished to disable said enabling means for a first period whereby said oscillator means is disabled for said first period, said flame sensing means enabling said enabling means for a second period to thereby enable said oscillator means to generate further voltage pulses, and means enabled by said enabling means whenever said oscillator means fails to produce voltage pulses during said second period to enable said energizing means to control said valve means to Interrupt the supply of fuel to said fuel outlet.
 6. A fuel ignition system as set forth in claim 5 which includes means for supplying a DC energizing potential to said ignition circuit to permit said enabling means to normally extend a DC enabling signal to said oscillator means, said oscillator means being responsive to said DC enabling signal to produce AC voltage pulses in an output circuit thereof, first means for coupling said voltage pulses to said electrode means to effect the generation of ignition sparks and second means for coupling said voltage pulses to said energizing means to permit energization of said valve means.
 7. A fuel ignition system as set forth in claim 6 wherein said oscillator means comprises semiconductor means, said first means comprising a transformer means having a first winding connected to extend siad DC enabling signal to a control input of said semiconductor means, a second winding connected to said electrode means, and third winding connected in an output circuit of said semiconductor means to permit said voltage pulses to be coupled to said second winding.
 8. A fuel ignition system as set forth in claim 5 wherein said flame sensing means includes switching means operable when enabled to inhibit said enabling means and timing means operable whenever a flame is established to enable said switching means for said first duration and to disable said switching means for said second duration.
 9. A fuel ignition system as set forth in claim 8 wherein said timing means includes capacitor means, first circuit means including said electrode means for permitting said capacitor means to charge over a first circuit path whenever a flame is established, and second circuit means including said switching means and said electrode means for permitting said capacitor means to discharge over a second circuit path to thereby operate said switching means, the discharge time of said capacitor means being greater than the charge time of said capacitor means whereby the first duration for which the oscillator means is inhibited is gerater than the second duration for which said oscillator means is enabled.
 10. A fuel ignition system as set forth in claim 6 wherein said energizing means includes control means having first switching means responsive to said voltage pulses to provide further pulses for energizing a control winding of said valve means for operating said valve means to supply fuel to said fuel outlet for ignition by said ignition sparks, and sampling means having second switching means and timing means responsive to said further pulses to energize a further control winding of said valve means to maintain said valve means operated when a flame is established.
 11. In a fuel ignition system including normally unoperated first valve means and normally operated second valve means connected in series between a fuel source and a fuel outlet, an ignition circuit for controlling the operation of said first and second valve means to supply fuel to said fuel outlet and for igniting fuel discharged by said fuel outlet, said ignition circuit comprising ignition means including first means operable when enabled to generate ignition sparks in the proximity of said fuel outlet for igniting fuel discharged by said fuel outlet to establish a flame, and second means for enabling said first means, energizing means controlled by said first means for effecting the operation of said first valve means, and sensing means operable whenever a flame is established to control said second means to disable said first means for a first period to thereby inhibit the generation of ignition sparks and to enable said first means for a second period to permit the generation of further ignition sparks, said ignition means including third means enabled by said second means whenever said first means fails to be enabled during said second period to effect deactivation of said second valve means to interrupt the supply of fuel to said fuel outlet.
 12. A fuel igniTion system as set forth in claim 11 which includes indicator means controlled by said energizing means to provide an indication each time a spark is generated.
 13. A fuel ignition system as set forth in claim 11 wherein said energizing means includes control means having first switching means enabled by said first means to energize a pickup winding of said first valve means to operate said first valve means to supply fuel to said fuel outlet for ignition by said ignition sparks, and sampling means including second switching means enabled by said first switching means to energize a hold winding of said first valve means to maintain said first valve means operated when a flame is established.
 14. A fuel ignition system as set forth in claim 11 wherein said energizing means includes control means having first switching means, said first means including means for generating control pulses to enable said first switching means to provide current pulses for effecting operation of said first valve means, said first switching means being disabled during said first period when the flame is established, and sampling means including second switching means and timing means responsive to said current pulses to provide a potential for enabling said second switching means to maintain said valve means operated during said first period.
 15. A fuel ignition system as set forth in claim 14 which includes third switching means energized by said first switching means to deactivate said second valve means whenever a flame fails to be established after a predetermined number of control pulses have been supplied to said first switching means by said first means.
 16. A fuel ignition system as set forth in claim 15 which includes indicator means energized by each current pulse provided by said first switching means.
 17. A fuel ignition system as set forth in claim 16 wherein said third means is enabled by said second means to continuously energize said second switching means whenever said first means fails to produce said control pulses during said second period to thereby effect continuous energization of said indicator means. 